Corona treatment is a method using an electrical corona discharge to modify a surface of a web to improve its ability to accept inks and adhesives. In a corona treatment, a high voltage electrode is mounted parallel to and spaced from a ground roller, which forms a grounded electrode. The air gap between the electrodes is energized, forming a corona, which, when web is passed therethrough modifies the material the web is formed of, and makes the web more receptive to ink and adhesives. Corona will be produced anywhere there is air within this air gap.
The occurrence known as “backside treat” is the result of a corona being produced on both sides of a web being treated, even though the corona treatment system is only intended to treat one side of the web. The resulting undesired treatment on the backside of the web may result in blocking and picking. The resulting undesired treatment on the backside of the web may also cause an insufficient treat level on the side of the web requiring treatment, since some the power intended for treating the web was delivered to the opposite side, thus, reducing the watt density provided to the side to be treated.
There are a number of causes for backside treat, all of which are the result of air being entrapped under the web being treated. One of the most common causes for backside treat is dirt buildup on the corona ground roll. Regardless if the corona treatment system is a bare roll or a covered roll, dirt buildup gets deposited on the surface of the ground roller. These uneven deposits of dirt buildup lift the web off the surface of the ground roller, entrapping air underneath the web. To eliminate backside treat caused by dirt buildup, the ground roller must be cleaned.